1. Field of the Invention
This invention is directed to an error detection and correction interface between a high speed data channel and a high capacity, high transfer rate digital data recording tape system.
2. Related Art
Error detection and correction is a significant problem in the area of high capacity, high transfer rate data recording systems, such as in an ID-1 unit of the type manufactured by Datatape Corporation (a subsidiary of Kodak), using a helical scan tape format. Errors can arise from magnetic-tape dropouts, electronic noise, dirt particles located between the head and tape, creases in the tape, oxide flaking, longitudinal scratches, oxide manufacturing flaws, faulty read/write electronics, etc. The present invention is directed to the correction of large error bursts, or dropouts, as well as smaller randomly occurring data errors. Both types of errors occur in helical scan magnetic tape formats, such as an ID-1 system. The teachings of the present invention are, however, also applicable to longitudinal tape formats.
Using various types of error detection and correction methods, wideband digital data can be reproduced f rom a digital recording system, such as an ID-1 system, with a bit error rate (BER) of less than one (1) in 10.sup.10 bits when averaged over 7.9.times.10.sup.11 bits, with the following restriction: according to the ANSI subcommittee that defined this standard, such a performance can be achieved excluding up to one error burst greater than 3k bytes per tape. Also, according to this subcommittee, one of ten tapes could have two or more such bursts, which would result in a BER significantly worse than one (1) in 10.sup.10 bits.
A typical prior art error correction system can be seen in U.S. Pat. No. 4,238,852 assigned to Sony Corporation. This system uses a linear, rather than a helical scan tape format, and optimizes the separation of the bits in only one dimension. Moreover, the separation between bits is not sufficient to overcome larger drop-out errors.
The present invention overcomes the limitations of such conventional tape drive data correction systems by way of a data translation method which rearranges the data on the recording tape in two dimensions, such that large error bursts, while they may destroy physically contiguous data groups, will not destroy logically contiguous data groups. Basically, the fundamental principle of the present invention is to separate as much as possible each bit of data composing a unique encoded data word correction group. The invention separates and physically spaces each bit both vertically and horizontally on the tape from its nearest logical bit neighbor. The present invention thus provides an additional layer of correction in addition to the correction system present already in high capacity tape drive systems. It is estimated that the present invention can correct error bursts of as much as 32k bytes every 100 megabytes.
Because of the increased reliability added by the present invention, it is expected to have wide use and application in many data processing applications requiring high transfer rates, high data density and high data integrity. Such applications include tape systems for large scale supercomputing facilities, digitally compressed HDTV, and high resolution computer display of data.